The present invention relates to high-power electrical switches, and in particular to a flexible cable operator for remotely actuating electrical switches such as circuit breakers.
High-power electrical circuitry is normally placed inside a metal cabinet to protect the electrical circuitry from the external environment and to shield users from potential hazards associated with the operation of the circuitry.
Often the cabinet provides a handle that serves both to lock a cabinet door and to disconnect electrical power from the interior circuitry before the door is opened. The handle may communicate through a flexible cable operator with a switch inside the cabinet, for example, a circuit breaker, so that when the handle is moved to allow opening of the cabinet door, the circuit breaker is also opened, removing electrical power from the interior circuitry. This feature is normally subject to the mechanical override in the event that the cabinet must be operated with the door open and the circuitry live.
A flexible cable operator provides a substantially incompressible sheath through which a flexible cable may slide. Opposite ends of the sheath are fixed respectively to a stationary structure of the handle and an actuator frame attached to the circuit breaker housing. One end of the cable is then attached to a movable portion of the handle to communicate this motion through the cable to a slider held within the actuator frame. The slider may provide a collar receiving a toggle operator of the circuit breaker to move the circuit breaker toggle between an “on” and “off” position with movement of the flexible cable by the handle.
The flexible cable must normally be “tuned” so that the motion at the circuit breaker is sufficient to move the circuit breaker toggle fully between on and off positions when the handle is moved between on and off positions. This tuning is normally accomplished by adjusting a pair of opposed “jam nuts” attached to a threaded barrel on one end of the flexible cable sheath. The jam nuts capture a flange of the actuator frame between them. By loosening one nut and tightening the other, the point of attachment of the sheath to the stationary actuator framework may be shifted to properly center the actuation range of the flexible cable with respect to the operating range of the circuit breaker toggle.
Adjusting these jam nuts can be relatively difficult requiring partial disassembly of the actuator framework and working within the close confines of that framework to loosen and tighten these two nuts. Once the end of the sheath is properly positioned, the two jam nuts must be tightened together using torque-controlled tools to ensure that the connection does not inadvertently loosen during vibration or use and to ensure that the torque is not so high as to damage the threaded barrel on the end of the sheath causing the sheath to separate from the actuator.
After moving the jam nuts, it can be difficult to determine whether the adjustment is correct because the handle may not be operated with the jam nuts loose such as would allow the sheath to move freely in this position tested. Accordingly multiple trials may be required for proper adjustment.